1. Field of the Invention
The present invention relates to grain moisture meters assemblies generally and particularly to portable grain moisture meters having back lit digital displays for indicating in full text the particular grain being tested and having inputs for calibrating the device to other meters as well as temperature compensation for the particular grain tested.
2. Description of the Prior Art
Portable grain testers utilizing the tested grain as a capacitance dielectric are known. Such devices utilize frequency attenuation through a constant volume of the dielectric as an indication of grain moisture. An example of such a device may be seen in U.S. Pat. Nos. 3,781,673 and 3,761,810. These devices in some cases even provided a limited digital display of the moisture content of the tested gain. However, these displays were limited to the moisture reading and did not provide a full text complementary digital readout of the particular grain being tested nor did they provide any biasing of the grain moisture readout to allow the operator to calibrate his device to the device that will measure the moisture content of the grain when it is transported to the elevator for sale. Also, there was no back lighting of the digital readout to allow the operator to use his device inside areas of limited visibility or outside in either early morning light or dusk conditions.
Since grain moisture sensors test grain at various times of the season or even day, the grain tested may have a wide range of temperatures. Temperature measurement of the grain in the testing device is thus necessary to properly compensate for these differing grain temperatures. Prior art devices as found in U.S. Pat. No. 4,688,332 have such temperature measurement and compensation. These devices additionally sense even the air temperature to provide a check on the actual grain temperature. However, none of these devices compensate for the effect of the actual test cell of the grain measuring device. The test cell acts as an overpowering temperature sink to mask the temperature of the grain or at least make this measurement vary depending on the position of the measuring device in the test cell. Thus the test cell temperature needed to be also measured and taken into consideration.
In view of the foregoing it will be seen that the prior art portable grain measuring devices did not provide an easily viewed extensive full text digital display of not only the moisture content of the grain but an accompanying legend of the actual grain being tested along with other complementary inputs and information such as the biasing of the moisture readout as well as the amount of bias. Also, prior art devices failed to properly compensate for the temperature of the test cell itself in their temperature compensation circuits.